[LLVMbugs] [Bug 3913] New: another miscompilation with -loop-index-split

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.org/bugs/show_bug.cgi?id=3913

           Summary: another miscompilation with -loop-index-split
           Product: libraries
           Version: trunk
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Scalar Optimizations
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: jay.foad at antixlabs.com
                CC: llvmbugs at cs.uiuc.edu


Created an attachment (id=2779)
 --> (http://llvm.org/bugs/attachment.cgi?id=2779)
test case

With the attached test case I get:

$ llvm-as -o - tiny2.ll | lli ; echo $?
0
$ llvm-as -o - tiny2.ll | opt -loop-index-split | lli ; echo $?
3

It's optimising:

  i = 0; do { if (i == 99) BODY; } while (++i != 10);

(which never executes BODY) into:

  if (99 > 0 && 99 != 10) BODY;

(which does execute BODY).


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